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How big is M31?

ollypenrice

By ollypenrice
in Imaging - Deep Sky

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ollypenrice

ollypenrice

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Our guests Sarah and Geoffrey fancied a go at M31 and I suggested that we add a bit of a theme to the project; go after the outer halo. To this end we shot seven 30 minute luminance subs (at F5) with 7 x 2 minute subs to control the core. I've previously worked with far more total data shot in 15 minute subs and am totally satisfied that this 7x30 minute set wiped the foor with earlier and longer runs in 15 minute subs. It was incredibly clean, took an insane stretch to catch the outer reaches of the galaxy and was fabulously noise free. There will be perennial debate over sub length but for me it will be water off a duck's back. The case is proven in my mind. Long subs sing from a dark site.

Colour came from a new run of  nearly 2 hours per channel plus the same again from older data. There's also about four hours Ha in here, some new and some old.

2 x Tak FSQ106N/Atik 11000, one setup courtesy of Tom O'Donoghue.

In this rendition the outer halo is the main target so we accepted, in the processing, that a softer stretch might look more balanced and ceratainly more familiar but this is about the halo. We wanted to find out where it was! My last M31 was a little 'hard' so I've kept this one softer.

Fortunately a new set of flats (shot through the green filter to a max value of  only 13000 counts but applied to all channels) proved to be nearly perfect and made separating the halo easy.

Full; http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2933351454&k=THqNDKQ&lb=1&s=O

M31%20outer%20halo%20FIN%20web-L.jpg

Olly

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JamesF

JamesF

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That is rather beautiful.

It seems quite odd that when viewing these three galaxies in a moderate aperture telescope they all appear to be some distance apart yet in this image M110 is almost hidden in the outer reaches of M31.  Conversely it's also fantastic to be aware, should one be able to see all three in the same field of view, that M31 easily occupies all the space between M32 and M110 and perhaps four or maybe even five times that across its width.

James

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ollypenrice

ollypenrice

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Erk!  What a beauty, Olly.

Is this living proof that read noise dominates sky background noise in really dark skies, so fewer longer subs wins under these conditions?

Adrian

It's all the proof I personally need, Adrian. I'll make the raw luminance data available shortly so folks can hava a go with it. It was so strong that we simply didn't have the colour to fill it despite the hours of colour data we had. This is only a partial application of the full luminance.

Geeeee.....

Olly, you really know how to take pretty pictures ;-)

Well done!

Hey, for once I had a scientific objective!!! :eek:   FInd that halo!  I vaguely remember hearing a part of it named as the something-or-other extension but so far I haven't found it again on the net. It might have been on the French forum though. Anybody?

Olly

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wxsatuser

wxsatuser

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It's all the proof I personally need, Adrian. I'll make the raw luminance data available shortly so folks can hava a go with it. It was so strong that we simply didn't have the colour to fill it despite the hours of colour data we had. This is only a partial application of the full luminance.

Geeeee.....

Olly, you really know how to take pretty pictures ;-)

Well done!

Hey, for once I had a scientific objective!!! :eek:   FInd that halo!  I vaguely remember hearing a part of it named as the something-or-other extension but so far I haven't found it again on the net. It might have been on the French forum though. Anybody?

Olly

Not saying this is the stuff but interesting reading.

http://www.ing.iac.es/PR/newsletter/news5/science1.html

http://www.stsci.edu/~kgilbert/M31.html

BTW

The full image is absolutely fantastic, sat here going round it looking at all the detail. :cool: :cool: :cool:

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PhotoGav

PhotoGav

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Oh yes, beautiful and wow, vibrant... So, that's what it's 'meant' to look like!

Out of interest, do you think a DSLR could ever get close to recording those colours?

I think I know the answer....

Well, it is Christmas soon...

And I have been a very good boy this year...

Dear Santa,

Please can I have a lovely CCD for my set-up....

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ollypenrice

ollypenrice

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Oh yes, beautiful and wow, vibrant... So, that's what it's 'meant' to look like!

Out of interest, do you think a DSLR could ever get close to recording those colours?

I think I know the answer....

Well, it is Christmas soon...

And I have been a very good boy this year...

Dear Santa,

Please can I have a lovely CCD for my set-up....

In a fast telescope I think a DSLR probably could get the colour, yes. Maybe even at F5 given the time. What it couldn't usefully do without cooling is the thirty minute sub. Star colour is also tricky in a DSLR. Probably short exposures are needed for that. I maintain that, for faint data, you really do need the long subs and the dark site.

Olly

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PhotoGav

PhotoGav

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In a fast telescope I think a DSLR probably could get the colour, yes. Maybe even at F5 given the time. What it couldn't usefully do without cooling is the thirty minute sub. Star colour is also tricky in a DSLR. Probably short exposures are needed for that. I maintain that, for faint data, you really do need the long subs and the dark site.

Interesting. Well, I'll be experimenting with my 60d over the coming months and hope to achieve some reasonable results. As for 'dark site', I'd be happy if I could just see the stars... This incessant cloud!

I look forward to the next Penrice Picture Post.

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ollypenrice

ollypenrice

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To the lower left, there does seem to be asymmetry - the halo bends up / out of the plane? :p

But perhaps indeed evidence of past interactions, galactic mergers referred above...

Yes. I looked at several other deep M31 images to confirm this finding. I think it's correct.

Olly

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